Jupiter’s moon Europa might harbor life in its vast water ocean below the thick ice crust. This deep subsurface habitat could potentially be investigated at locations of active outgassing, giving the question whether Europa is geologically active a crucial importance.
Evidence for present-day activity remained, however, elusive for decades. In 2012, spectral images taken with HST/STIS showed local UV emissions from hydrogen and oxygen, interpreted as water vapor aurora from active outgassing or plumes. Thereafter several studies derived the existence of water plumes on various locations. These studies used a variety of methods like UV transit imaging with HST, IR emission spectra with the Keck telescope, and archived in-situ spacecraft data. I will review the different studies claiming evidence and explain why unambiguous evidence is still missing!